The 5 Million population of Jordan, is distributed on 8.9 million Ha. of land from which only 2.6% under agriculture and 700,000 Ha, “Marginal lands”, potentially arable, but water deficits limit their use in this Mediterranean climate.

The objective was to identify and evaluate representative soils of Jordan, based upon their soil taxonomy, for sequestering additional carbon.

Existing field, laboratory data, developed at major universities, research centers of Jordan were obtained and utilized through collaborative projects with Jordanian scientists.

A total of ten pedons (four of the most dry and two in each of three subsequent 100-250, 250-400 and 400- 650 mm annual rainfall regions) were selected on a Climo-toposequence at elevations ranging from 500 to 1850 meters a.s.l. These soils were developed on cherty limestones associated with basalt parent materials. Moisture regimes varied from aridic to xeric and textures from loamy to very fine at the family level. Soils were classified within calciorthids, haplargids, paleoxeralfs, chromoxererts subgroups.

Carbonates increased with depth but, average amounts within the control section decreased from 38% to 9% . Slight increases of lime in some surface layers might be due to aeolian activities. Carbonates are mostly combined with the silt fractions from drier regions at the lower elevations and with sand fractions of more humid-soils at higher elevations.

Organic carbon ( OC ) decreased with depth throughout pedons but, in contrast with accepted knowledge, OC contents in surface horizons increased from 0.75 to 1.38% in regions from more humid to drier soils in this study. This new finding appears to result from greater vegetative growth of hallophytic biomass, observed in dry regions.

Further studies needed to evaluate potentiality of arid/semiarid soils as a possible C-sink in relation to agronomic practices that promote sequestration of atmospheric C through enhanced efficiency of salt water use.